"Unfinished" is often popular to keep a lower property tax value. Property taxes are high in Texas due to no personal income taxes.
Add sheetrock and paint and now it is a "living space" and not just storage utility area.
There seems to be plenty of insulation in the side walls/roof and a big whole house cooling/heating system right there, to tap in to if needed.
In California, we have often no basements or usable attic spaces so a "California Basement" is usually a converted garage.
Most homeowners never get permits or inspections of their converted spaces or "sheds" due huge local fees and higher property taxes too.
